Due in part to the lack of transplant availability, many patients with end-stage renal disease receive regular hemodialysis treatments. To minimize treatment time, hemodialysis requires a large blood volume flow rate that is typically achieved through the surgical creation of an arteriovenous shunt. This creates a low resistance pathway that results in significantly increased flow rates through a graft or an arteriovenous fistula (AVF). After surgical creation of an AVF, the inflow and outflow vessels must dilate sufficiently, and the venous tissue must undergo a remodeling process known as “fistula maturation” in order to be able to sustain the high flow rates necessary for hemodialysis. One common problem with AVFs is tissue proliferation along the lumen of the vein known as neointimal hyperplasia (NIH), which can lead to stenosis, reduced flow, and ultimately failure of the fistula. The progression of NIH may be, in part, the venous tissue's response to the abnormal hemodynamic stresses which result from the increased flow rates and large pressure drop across an arteriovenous anastomosis. The abnormal flow through an AVF appears to be generally turbulent rather than laminar.
Several reports suggest that the native state of arterial blood flow may exhibit circumferentially oriented velocity components such that the blood flow is helical or spiral in nature. The spiral blood flow is thought to play a roll in maintaining healthy vascular function. Thus, it may be possible that creating spiral blood flow in the vicinity of an AVF could help prevent or slow the progression of NIH.
One aspect of fistula maturation is significant venous dilation up to roughly 150% of the vein's original diameter. While there are several devices known for inducing spiral blood flow, some of them have fixed diameters rendering them unsuitable to accommodate vessel diameter changes due to fistula maturation. Other spiral flow devices that can accommodate a variable diameter typically include a spiral blood flow inducing structure that changes in its helix angle geometry with changes in the diameter of the device. One example in this regard is taught in U.S. Pat. No. 7,682,673. This change in the spiral inducing properties of the device may be undesirable, and may cause the device to diverge away from some desired helix angle.
The present disclosure is directed toward one or more of the problems set forth above.